There is nothing like being strapped to a medical table, then having your entire body slide head first into a large sci-fi-looking machine with a 2.5-foot-wide hollow tube at its centre, to focus the mind.
Once inside this modern-day sarcophagus, the disembodied robotic voice of a technician asks if you are “comfortable,” then instructs you to lie perfectly still. If you were thinking of doing yoga, forget it. Well, savasana (corpse pose) is probably fine.
Then, accompanied by the strains of Vivaldi, the scanning process begins, and all manner of strange mechanical and electrical hums, rumbles, and whines begin, continuing for the next 30 minutes.
To quell the claustrophobic sensation (and the rising sense of panic) I experience during this time, I force my mind to focus. I find myself wondering what exactly it is that is going on around me. I’m inside an MRI scanner, but what exactly is an MRI scanner? What are these strange forces it creates that can apparently permeate my body at the atomic level and create high-resolution imagery of my internal anatomy? Why am I unable to feel anything (other than rather scared)? What actually is an MRI scan?
Later, back in the surgery, when viewing the imagery on a computer screen along with my consultant, I marvel at the lateral and longitudinal sections of my spinal column. He zooms in, out, back, and forth from crown to coccyx with a flick of the middle mouse wheel, and he eventually focuses on a set of three of my discs, which confirms to my doctor his correct diagnosis of herniation at L4 and L5 in my lower back.
I must look worried, because he tells me the prognosis is actually rather good, and it doesn’t require surgery. He says not to worry and that my insurance “should” cover all the costs.
He turns out to be right on both counts, which is just as well. But when I receive the invoice, my heart skips a beat or two at the size of the bill (which is well into the several thousands), and I find myself wondering again what exactly is it about an MRI scan that makes it so expensive.
I decide to do some research. What exactly is an MRI Scanner? How does it work? What does one cost?
It turns out the answers to these questions are both simple and complex. And since we have limited space here, I will attempt to give some brief answers to these overwhelmingly popular questions.
What does MRI stand for?
Magnetic resonance imaging.
What is an MRI scanner?
It’s basically a HUGE electromagnet in the form of a torus (like a doughnut with a hole in the middle, which is the hole your body goes into). The huge electromagnet is capable of creating a magnetic field of between 2-3 teslas is surrounded by smaller electromagnets, which focus the magnetic field of the huge magnet onto the area of interest. It also includes several radio transmitters/receivers, which essentially pick up the signals emitted when the magnetic field interacts with the molecules of the human body.
How does an MRI scanner work in principle?
Essentially, we humans are mostly made of water—hydrogen and oxygen. Under the influence of a magnetic field , these molecules will align their polarity with that of the field so that they all point in the one direction (or the other). The scanner also produces a radio frequency current that creates a varying magnetic field. The protons in the hydrogen and oxygen molecules absorb the energy from the magnetic field and flip their spins. When the field is turned off, the protons gradually return to their normal spin, which is a process called precession. The return process produces a radio signal that can be measured by receivers in the scanner, and it is these signals which (with the help of some rather sophisticated software) are then interpreted and made into an image.
Gosh! All those electromagnets/radio transmitters must use an awful lot of electricity?
Indeed they do. So much, in fact, that were they to run under “normal” conditions, the energy requirement would be so large as to be both impractical and uneconomic, to say the least. To get around this inconvenient truth, the magnets in an MRI scanner are cooled to supercool temperatures (-263 Kelvin) by encasing them in a jacket of liquid helium. At such low temperatures, the copper wire coils of the magnet essentially become superconductors, meaning that they continue to function as electromagnets even after the power is turned off.
So, an MRI Scanner is basically just a HUGE doughnut-shaped magnet inside a BIG fridge?
Well, that’s simplifying it a bit, but yes, that’s about right?
But aren’t electromagnets mainly just lots of turns of copper wire?
And I can buy a fridge (made in China) for less than $100.
True, but this really is a super cool (sorry about the awful pun) fridge. They tend to be a bit pricier.
So why is an MRI machine so expensive?
Surprisingly, it isn’t necessarily so. Of course, it’s all relative and dependant on the size and power of the scanner you wish to purchase. There was a rule of thumb that said an MRI scanner cost approximately the same millions of dollars as the scanner’s field strength. So a 1.5 T scanner cost around 1.5 million dollars, a 3 T cost 3 million, and so on. If you watch a video of the manufacturing of an MRI machine, you will begin to appreciate the sophisticated engineering, environmental control, and technology required for the assembly of these beasts. It’s not something you can knock up in your average garden shed. However MRI, scanners have been around long enough now that there is a flourishing used MRI scanner market, with prices starting around the far more reasonable $150K for a used working 1.5 T machine.
Wow! I think I will order one now and go into business with an MRI booth, printing t-shirts of peoples’ insides!
Steady on. You’re forgetting the cost of construction and infrastructure to house your purchase. An MRI scanner requires a specially reinforced lead-shielded room and a so-called Faraday cage in order to keep all the stray RF out, so the scanner can detect the RF emitted by your hydrogen nuclei. The construction cost of such a room could easily exceed the cost of your “budget” scanner by several hundred thousand dollars—or more if it is not located on the ground or basement floor.
Well, maybe I could save on costs by fitting/running things myself?
Not really. In fact, the transportation and installation costs for a used scanner being added to a scanner-ready room is a rather complex logistical operation, requiring refrigerated transportation and more. That, again, can easily run into the hundreds of thousands. Then, don’t forget there’s the cost of keeping the magnet filled with liquid helium to maintain superconductivity, which could easily still cost you about 10,000 dollars a year if you don’t have a good cryomechanic.
Add to this the specialist computer hardware and software and the associated (highly trained) radiologists required to successfully run your scanner, and you can begin to see why that scan invoice came into the several thousands of dolYou’re going to have to print a few t-shirts before you see a profit.